Among the various video display systems available in the art, an optical projection system is known to be capable of providing high quality displays in a large scale. In such an optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N, actuated mirrors, wherein each of the mirrors is coupled with each of the actuators. The actuators may be made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electric field applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture of, e.g., an optical baffle. By applying an electric signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as a projection lens, to thereby display an image thereon.
In FIG. 1, there is illustrated a cross sectional view setting forth an array of M.times.N thin film actuated mirrors 100, wherein M and N are integers, disclosed in a copending commonly owned application, now U.S. Pat. No. 5,757,539, entitled "THIN FILM ACTUATED MIRROR ARRAY FOR USE IN AN OPTICAL PROJECTION SYSTEM".
The array 100 includes an active matrix 110, a passivation layer 116, an etchant stopping layer 118 and an array of M.times.N actuating structures 120.
The active matrix 110 includes a substrate 112, an array of M.times.N transistors (not shown) and an array of M.times.N connecting terminals 114. Each of the connecting terminals 114 is electrically connected to a corresponding transistor in the array of transistors.
The passivation layer 116, made of, e.g., a phosphor-silicate glass (PSG) or silicon nitride, and having a thickness of 0.1-2 .mu.m, is located on top of the active matrix 110.
The etchant stopping layer 118, made of silicon nitride, and having a thickness of 0.1-2 .mu.m, is positioned on top of the passivation layer 116.
Each of the actuating structures 120 has a distal and a proximal ends, and further includes a tip (not shown) at the distal end thereof and an etching aperture (not shown) traversing vertically therethrough. Each of the actuating structures 120 is provided with a first thin film electrode 132, a thin film electrodisplacive member 126, a second thin film electrode 124, an elastic member 122 and a conduit 128. The first thin film electrode 132 made of an electrically conducting and light reflecting material, e.g., aluminum(Al) or silver(Ag), is located on top of the thin film electrodisplacive member 126, and is divided into an actuating and a light reflecting portions 130, 140 by a horizontal stripe 134, wherein the horizontal stripe 134 disconnects electrically the actuating and the light reflecting portions 130, 140. The actuating portion 130 thereof is electrically connected to ground, thereby functioning as a mirror as well as a common bias electrode. The light reflecting portion 140 thereof functions as the mirror. The thin film electrodisplacive member 126, made of a piezoelectric material, e.g., lead zirconium titanate(PZT), or an electrostrictive material, e.g., lead magnesium niobate(PMN), is placed on top of the second thin film electrode 124. The second thin film electrode 124, made of an electrically conducting material, e.g., platinum/tantalum(Pt/Ta), is located on top of the elastic member 126, and is electrically connected to a corresponding transistor through the conduit 128 and the connecting terminal 114, wherein the second thin film layer 124 is iso-cut into an array of M.times.N second thin film electrodes 124 by using a dry etching method such that each of the second thin film electrodes 124 is electrically disconnected from other second thin film electrodes 124 (not shown), thereby allowing it to function as a signal electrode. The elastic member 122, made of a nitride, e.g., silicon nitride, is positioned below the second thin film electrode 124. A bottom portion at the proximal end thereof is attached to top of the active matrix 110, with the etchant stopping 118 and the passivation layers 116 partially intervening therebetween, thereby cantilevering the actuating structure 120. The conduit 128, made of a metal, e.g., tungsten(W), extends from top of the thin film electrodisplacive member 126 to top of a corresponding connecting terminal 114, thereby connecting electrically the second thin film electrode 122 to the connecting terminal 114. The conduit 128 extending downward from top of the thin film electrodisplacive member 126 and the first thin film electrode 132 placed on top of the thin film electrodisplacive member 126 in each of the thin film actuated mirrors 150 are not electrically connected to each other.
There are certain shortcomings associated with the above described array 100 of M.times.N thin film actuated mirrors 150, one of the shortcomings being the possible occurrence of a short-circuit between the first and the second electrodes 132, 124 in each of the actuated mirrors 150. In the array, since the conduit 128 in each of the thin film actuated mirrors 150 extends from the corresponding connecting terminals to top of the electrodisplacive member 126, an extreme care is required during patterning of the first thin film electrode 132. The first thin film electrode 132 must electrically be disconnected completely from the conduit 128 in each of the thin film actuated mirrors 150. If not, it may lead to an establishment of an electrical connection between the first thin film electrode 132 and the second thin film electrode 124, resulting in a short-circuit therebetween.